Has your application disappeared from the list in SiteAdmin, but you can still login to the application?
Most likely you have converted it to a Template by Accident.
1. Login to SiteAdmin
2. Go to "Applications" (top menu)
3. Select the "Templates" radio button.
Now you should be able to see the application.
4. Select the application.
5. Scroll down to and expand "Template"
6. Click "Convert to Application"